BG113408A - Force and torque measuring device - Google Patents

Abstract

The force and torque measuring device consists of a first element (1) and a second element (2) positioned so that they are juxtaposed to one another, and four legs (3, 4, 5 и 6) which connect the two elements (1) and (2) and are situated evenly on the periphery of the two elements (1) and (2) and between the said elements. Four brackets (7, 8, 9 and 10) are evenly positioned over the periphery of the first element (1). Evenly situated on the periphery of the second element, there are four other brackets (11, 12, 13 and 14) which are pointed to the brackets (7, 8, 9 and 10) of the first element (1), but do not come in contact with them. Between bracket (7) and its corresponding bracket (11) there are a crosswise MEMS sensor (15) and a lengthwise MEMS sensor (16). Between bracket (8) and its corresponding bracket (12) there are a crosswise MEMS sensor (17) and a lengthwise MEMS sensor (18). Between bracket (9) and its corresponding bracket (13) there are a crosswise MEMS sensor (19) and a lengthwise MEMS sensor (20). Between bracket (10) and its corresponding bracket (14) there are a crosswise MEMS sensor (21) and a lengthwise MEMS sensor (22). The one end of each crosswise and each lengthwise MEMS sensor is fixed on a bracket of element (1) and its other end is fixed on a bracket of element (2). The force and torque measuring device can be used for measuring the load on the tool of a metal cutting machine or on the effectuator unit of a robot, in industrial processes such as cutting or processing of metals, in installation works as well as in the area of human training and interaction with collaborative robots and exoskeletons.

Description

Device for measuring forces and moments

Field of technique

The present invention relates to a device for measuring forces and torques applied to an extension unit of a robot or a metal-cutting machine. A device will find application for measuring forces and moments in technological processes such as assembly, cutting and processing of metals, etc. Also, the device could find application in exoskeletons and collaborative robots in learning and human interaction.

Prior art

A "Six-axis force sensor [1] is known, consisting of two elements located in opposite positions to each other and four legs located evenly between the two elements along their periphery which connect the two elements and which deform elastically as a result of applying a load to one of the two elements, thus allowing the measurement of forces and moments acting on one of the two elements, based on the detected deformations generated in the legs. In this, each leg is shaped as a T-leg, consisting of a transverse beam extending in a circumferential direction connected at both ends to one element and a vertical beam perpendicular to the transverse beam connected to the other element. Leg deformations are detected by a first uniaxial strain gauge and a second uniaxial strain gauge, the first uniaxial strain gauge being attached to the surface of the cross beam facing the side opposite the vertical beam or to the surface of the cross beam facing the vertical beam so that it can to detect strain generated in the cross beam in the longitudinal direction. The second uniaxial strain gauge is attached to a side surface of a vertical beam so that it can detect strain generated in the vertical beam in a circumferential direction.

A disadvantage of the Six-Axis Force Sensor is that it is sensitive to noise due to the rigid mechanical construction with small deformations being sensed by strain gauges. Also, to accurately measure the deformations, it is necessary to attach the strain gauge at a certain point where the deformations are most pronounced.

Technical essence

The task of the invention is to create a device for measuring forces and torques, which is insensitive to noise when reading the forces and moments, has a simplified construction that is easy to manufacture.

The task is solved with a device for measuring forces and torques, consisting of two elements located in opposite positions to each other and four legs located evenly between the two elements along their periphery, which connect the two elements and which deform elastically due to the application of load to one of the two elements. To the first element, four consoles are evenly spaced along its periphery, which are directed towards the other element. To the second element, four other consoles are evenly spaced along its periphery, which are directed to the consoles of the first element without touching them.

The first pair of matching brackets are located midway between the first leg and the second leg. The second pair of matching brackets are located midway between the second leg and the third leg. The third pair of matching brackets are located midway between the third leg and the fourth leg. A fourth pair of matching brackets is located midway between the fourth leg and the first leg.

A transverse MEMS (micro electro mechanical system) sensor and a longitudinal MEMS sensor are located between each of their respective cantilevers, one end of each sensor being fixedly attached to the cantilever of a first element and the other end of each sensor being fixedly attached to the cantilever of a second element.

The transverse MEMS sensor produces a signal proportional to the positional deviation created by the applied load of the first element relative to the second element in the transverse /tangential/ direction. The longitudinal MEMS sensor produces a signal proportional to the positional deviation created by the applied load of the first element relative to the second element in the longitudinal direction /along the axis of the device/. The applied load is a force or moment that causes elastic deformations in the four legs and a deflection of the first member relative to the second, causing each cantilever of the first member to deflect relative to the corresponding cantilever of the second member. Movements in the longitudinal or transverse direction between the corresponding consoles are recorded by the MEMS sensors located on them, as a change in the output voltage, proportional to the movement in the longitudinal or transverse direction.

An advantage of the device for measuring forces and torques is its insensitivity to noise, since the sensors are mounted on the rigid elements and are independent of the elastic legs and the distribution of stresses and deformations on them. The device has a simplified monolithic construction that is easy to manufacture by cutting or electro erosion.

Description of attached figures

The invention is better explained by the following attached figures, where:

Figure 1 is a general view from one side of the device for measuring forces and moments.

Figure 2 is a general view from the other side of the device for measuring forces and moments.

Figure 3 is a longitudinal section of the device for measuring forces and moments.

Example implementation

The invention is better explained by the following example.

The device for measuring forces and torques consists of two elements 1 and 2 located in an opposite position to each other and four legs 3, 4, 5 and 6 located evenly between the two elements 1 and 2 along their periphery, which connect the two elements 1 and 2. To the first element 1, four consoles 7, 8, 9 and 10 are uniformly located along its periphery, which are directed to the second element 2. To the second element 2, four other consoles 11, 12, 13 and 14 are uniformly located along its periphery , directed to the brackets 7, 8, 9 and 10 of the first element 1 without touching them. The first bracket 7 of the first element 1 and the first bracket 11 of the second element 2 are located midway between the first leg 3 and the second leg 4. The second bracket 8 of the first element 1 and the second bracket 12 of the second element 2 are located midway between the second leg 4 and third leg 5. Third bracket 9 of first element 1 and third bracket 13 of second element 2 are located midway between third leg 5 and fourth leg 6. Fourth bracket 10 of first element 1 fourth bracket 14 of second element 2 are located in the middle between the fourth leg 6 and the first leg 3. The first transverse MEMS sensor 15 and the first longitudinal MEMS sensor 16 are attached at one end to the first bracket 7 of the first element 1 and at the other end to the first bracket 11 of the second element 2. A second transverse MEMS sensor 17 and a second longitudinal MEMS sensor 18 are attached at one end to a second bracket 8 of the first element 1, and at the other end to a second bracket 12 of a second element 2. A third transverse MEMS sensor 19 and a third longitudinal MEMS sensor 20 are closed pen at one end on a third bracket 9 of the first element 1 and at its other end on a third bracket 13 of the second element 2. A fourth transverse MEMS sensor 21 and a fourth longitudinal MEMS sensor 22 are attached at one end on a fourth bracket 10 of first element 1, and at its other end on the fourth bracket 14 of the second element 2.

Use of the invention

The invention can be used in the following way. The device is placed on a robot or metal-cutting machine, and the second element 2 is fixedly fixed to the robot or machine with bolts. A robot gripper or a metal-cutting machine tool is attached to the first element 1 using bolts.

When an arbitrary spatial load is applied to the gripper or tool, this load is transmitted to the first element 1, resulting in elastic deformations in the four legs 3, 4, 5 and 6 which connect element 1 to element 2. As a result element 1 deflects relative to element 2, causing all cantilevers 7, 8, 9, and 10 of element 1 to deflect relative to the corresponding cantilevers 11, 12, 13, and 14 of element 2. The displacements of the corresponding cantilevers are transmitted to the two opposite ends of MEMS sensors located on them.

Transverse MEMS sensors 15, 17, 19, and 21 have a sensitive part that is up to 3 mm wide and 12 µm to 270 µm thick. This part is an elastic silicon wafer with a suitable geometry, including 4 piezoresistors connected in a bridge circuit. The deformation of the silicon wafer leads to a proportional change in the output voltage proportional to the displacement in the transverse direction.

Longitudinal MEMS sensors 16, 18, 20, and 22 have a sensing portion that is up to 3 mm wide and 12 µm to 270 µm thick. This part is an elastic silicon wafer with another suitable geometry, including 4 piezoresistors connected in a bridge circuit. The deformation of the silicon wafer leads to a proportional change in the output voltage proportional to the displacement in the longitudinal direction.

Thus, from the eight MEMS sensors 15, 16, 17, 18, 19, 20, 21, and 22, 8 voltages vl, v2, v3, v4, v5, v6, v7, v8 are read, which can be combined into the vector

V = [vl, v2, v3, v4, v5, v6, v7, v8] ^T

These stresses are determined by transverse and longitudinal displacements generated by various forces and moments.

In the most general case, the spatial load of element 1 can be represented by three forces Fx, Fy, Fz and three moments: Mx, Mu, Mz along the axes of the Cartesian coordinate system OXYZ, the center of which O is located in the center of the device and the axis X coincides with the drive axis. The load can be represented by the vector F:

F = [ Fx, Fy, Fz, Mx, My, Μζ] ^τ

The relationship between the power loads F and the received voltages from the sensors V can be found by correlation [1] using the equation

F = CV (1)

Where C is a calibration matrix ^C P ^with 12 - ^with 18 with = ^C2 ' .........

_ ^with 61 ...... ^with 68_

The calibration matrix C can be obtained experimentally by applying different loads F and making multiple recordings of the voltages V of the eight MEMS sensors. Once the relationships between F and V are known, one can use equation (1) and the method of least squares as suggested in [1] to obtain the matrix C. Once the calibration matrix is known, the six can be measured components of spatial forces and moments by reading the readings of the eight MEMS sensors 15, 16, 17, 18, 19, 20, 21, and 22 and using equation (1).

Claims (1)

1. Device for measuring forces and torques consisting of two elements /1 / and /2/ located in opposite positions to each other and four legs /3/, /4/, /5/ and /6/ connecting the two elements /1/ and /2/ and evenly spaced between the two elements /1/ and /2/ along their periphery, characterized by the fact that four consoles /7/, /8/, / are evenly spaced to the first element /1/ 9/ and /10/ on its periphery and to the second element /2/ four other brackets /11/, /12/, /13/ and /14/ are evenly located on its periphery, directed to the brackets /7/, /8 /, /9/ and /10/ of the first element /1/ without touching them, with the first bracket /7/ of the first element /1/ and the first bracket /11/ of the second element /2/ located midway between first leg /3/ and second leg /4/, second bracket /8/ of first element /1/ and second bracket /12/ of second element /2/, are located midway between second leg /4/ and third leg / 5/, third console /9/ of first element/1/ and third console /13/ of second element /2/ are n midway between third leg /5/ and fourth leg /6/, fourth bracket /10/ of first element /1/ fourth bracket /14/ of second element /2/ are located midway between fourth leg /6/ and first leg /3/, also a first transverse MEMS sensor /15/ and a first longitudinal MEMS sensor /16/ are attached at one end on a first bracket /7/ of a first element /1/ and at the other end on a first bracket / 11/ of a second element /2/, also a second transverse MEMS sensor /17/ and a second longitudinal MEMS sensor /18/ are attached at one end on a second bracket /8/ of a first element /1/, and at the other end on a second bracket /12/ of a second element /2/, also a third transverse MEMS sensor /19/ and a third longitudinal MEMS sensor /20/ are attached at one end on a third bracket /9/ of a first element /1/, and at its other end on a third bracket /13/ of a second element /2/, also a fourth transverse MEMS sensor /21/ and a fourth longitudinal MEMS sensor /22/ are attached at one end on a fourth horse base /10/ of the first element /1/, and at its other end on a fourth bracket /14/ of the second element /2/.